US4412849A - Method and apparatus for control of gas-borne particulates - Google Patents

Method and apparatus for control of gas-borne particulates Download PDF

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Publication number
US4412849A
US4412849A US06/323,571 US32357181A US4412849A US 4412849 A US4412849 A US 4412849A US 32357181 A US32357181 A US 32357181A US 4412849 A US4412849 A US 4412849A
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axis
gas
parallel
air
axes
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Expired - Lifetime
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US06/323,571
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English (en)
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Chandru M. Shahani
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Klenzaids Engineers Private Ltd
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Klenzaids Engineers Private Ltd
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Priority claimed from GB8111175A external-priority patent/GB2098317B/en
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Assigned to KLENZAIDS ENGINEERS PRIVATE LIMITED reassignment KLENZAIDS ENGINEERS PRIVATE LIMITED ASSIGNMENT OF ASSIGNORS INTEREST. Assignors: SHANHANI, CHANDRU M.
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F24—HEATING; RANGES; VENTILATING
    • F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
    • F24F3/00—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems
    • F24F3/12—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling
    • F24F3/16—Air-conditioning systems in which conditioned primary air is supplied from one or more central stations to distributing units in the rooms or spaces where it may receive secondary treatment; Apparatus specially designed for such systems characterised by the treatment of the air otherwise than by heating and cooling by purification, e.g. by filtering; by sterilisation; by ozonisation
    • F24F3/163—Clean air work stations, i.e. selected areas within a space which filtered air is passed
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
    • B01D46/10—Particle separators, e.g. dust precipitators, using filter plates, sheets or pads having plane surfaces
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D46/00—Filters or filtering processes specially modified for separating dispersed particles from gases or vapours
    • B01D46/52—Particle separators, e.g. dust precipitators, using filters embodying folded corrugated or wound sheet material
    • B01D46/521—Particle separators, e.g. dust precipitators, using filters embodying folded corrugated or wound sheet material using folded, pleated material
    • B01D46/522—Particle separators, e.g. dust precipitators, using filters embodying folded corrugated or wound sheet material using folded, pleated material with specific folds, e.g. having different lengths
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S55/00—Gas separation
    • Y10S55/18—Work bench
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S55/00—Gas separation
    • Y10S55/29—Air curtains

Definitions

  • the present invention relates to a method of controlling gas-borne particulates, and more particularly, but not exclusively, to controlling the migration and deposition of contaminating airborne particulates. It further relates to apparatus for achieving such control which may be used, for example, to obtain a work space substantially devoid of airborne particulate contaminants, both biological and non-biological, such as is necessary for the manufacture of sterile pharmaceutical products and micro-electronic components. Another use is in hospitals, where isolation of patients and prevention of contamination during surgical procedures is intended.
  • Previously proposed airborne contamination control methods include the widely used Laminar Air Flow System for equipment like work stations and sterilizing tunnels, and also for clean or sterile rooms. These rely on airflow in which the entire body of air within a confined area essentially moves with uniform velocity along parallel flow lines. This velocity through the cross section of the work space, is normally maintained at 27.5 meters per minute with a uniformity within plus or minus 20%. When the airflow is vertically downward this velocity can be lower, but with the uniformity maintained. The intention is to stratify the air such that minimum cross-stream particulate migration occurs, with the result that activity-generated particulates that become airborne are carried linearly along a predictable path.
  • the hitherto proposed uniform velocity laminar air flow systems are also liable to be affected by particulate migration caused by different energy gradient forces. Free particulates travel to the region where the energy level is lowest. For example, particulates settle under the influence of gravity; and, where a thermal gradient exists, particulates tend to move towards the cooler zone; and statically charged particulates move towards a neutralising field. In practical work situations, a single uniform velocity does not effectively counter all these energy differentials.
  • one feature of the invention resides in providing a laminar flow of gas wherein the flow velocity of adjacent streamlines of gas within the flow varies in at least one direction transverse to the flow.
  • a final filter which has a tapering formation and comprises a plurality of pleats, with each successive pleat run being progressively and incrementally greater, and thereby with a larger surface area; which, with a constant media traverse air velocity, gives rise to a graded pressure differential at the projected face; thus yielding a correspondingly graded exit air velocity profile.
  • FIG. 1 is a perspective view, partially cross-sectioned, which shows the basic elements in position, of one embodiment according to the present invention arranged in a horizontal air flow configuration where the velocity gradient is along both the horizontal and vertical axes;
  • FIG. 2 is a fragmentary schematic view illustrating the different axes of operation in relation to the filtering device and a bluff object obstructing the air flow graded as per FIG. 1;
  • FIG. 3 is similar to FIG. 1, wherein the filtering device is positioned to convey air flow in velocities graded along the vertical axis;
  • FIG. 4 corresponds to FIG. 2, with the air flow graded along the vertical axis;
  • FIG. 5 represents Bernoulli's principle
  • FIG. 6 is a fragmentary schematic plan view of a beaker placed in the path of a uniform velocity air flow
  • FIG. 7 is a fragmentary schematic view in elevation, with the beaker in uniform velocity air flow
  • FIG. 8 is a view corresponding to FIG. 6, with the same beaker placed in air flow graded along the horizontal axis;
  • FIG. 9 corresponds to FIG. 7, with the air flow velocities graded along the vertical axis and increasing in the direction of the working table;
  • FIG. 10 is a perspective view similar to FIG. 1, of another embodiment where the air flow is in a vertical direction, with the velocity gradient along the horizontal axis;
  • FIG. 11 is a fragmentary schematic view showing the different axes of operation in relation to a filtering device and a bluff object in the path of graded velocity air stream flowing vertically down;
  • FIG. 12 is a fragmentary schematic view in elevation of the streamlines around a bluff object in a graded air flow directed vertically;
  • FIG. 13 corresponds to FIG. 12, but in a uniform velocity air flow
  • FIG. 14 shows the trajectories followed by particles of various sizes when released in a uniform velocity air flow
  • FIG. 15 corresponds to FIG. 14, with the same particles in a graded velocity air flow
  • FIG. 16 is a cross-section in side-elevation of one form of apparatus for sterilizing objects
  • FIG. 17 shows curves of the temperature cycles that the objects exhibit in the apparatus as per FIG. 16;
  • FIG. 18 is a perspective view of another form of filtering device having instrumentally for generating air streams of graded velocities along both the ⁇ Y ⁇ and ⁇ Z ⁇ axes, with one side partly sectioned;
  • FIG. 19 is a detail of the device as per FIG. 18;
  • FIG. 20 graphically shows the velocity curves of the filtering device per FIG. 18.
  • the width of the airstream arrows F is, in all Figures, in proportion to the velocity of the airstream associated with that arrow.
  • FIG. 1 schematically illustrates one embodiment of the invention which comprises a work space W having a particulate density of less than three particles of 0.5 micron per liter of air, this being achieved by a device comprising a filter 1 that filters and in addition conveys air in streamlines F of graded velocities from 20 meters per minute to 40 meters per minute; a blower 2 having an air intake through a coarse filter 3 and delivering air to a plenum 4 under sufficient pressure to get a single uniform traverse velocity of 2 to 3 meters per minute across the medium 5 from which the filter pleats are formed.
  • a device comprising a filter 1 that filters and in addition conveys air in streamlines F of graded velocities from 20 meters per minute to 40 meters per minute; a blower 2 having an air intake through a coarse filter 3 and delivering air to a plenum 4 under sufficient pressure to get a single uniform traverse velocity of 2 to 3 meters per minute across the medium 5 from which the filter pleats are formed.
  • the rate of flow is determined by the area of each pleat which successively and progressively increases from one pleat to the next along the ⁇ Y ⁇ and ⁇ Z ⁇ axes.
  • FIG. 2 which also shows axis ⁇ X ⁇ as the direction of air flow which is perpendicular to the plane represented by ⁇ Y ⁇ and ⁇ Z ⁇ axes.
  • ⁇ U ⁇ is the magnitude of the velocity of air flow.
  • a and b can assume any value, or a succession of values, between minus infinity and plus infinity, provided a and b are not both zero.
  • FIG. 3 shows a configuration similar to the one shown in FIG. 1, wherein the filtering device 1 is constructed and positioned such that the velocity gradient is along the ⁇ Z ⁇ axis and increases in magnitude as it nears the table surface 7.
  • FIG. 5 depicts the principle of conservation of energy, as quantified by Bernoulli's equation.
  • ⁇ A ⁇ represents any point upstream of the object where flow is steady, fully developed and time invariant.
  • ⁇ B ⁇ is the point of impaction on surface dA.
  • the angle of incidence 0
  • the entire kinetic head of a streamline converts to an equivalent pressure head and ⁇ B ⁇ is a point of stagnation.
  • a bundle of similarly impacting streams on a flat surface yield a corresponding bundle of stagnation points.
  • a uniform velocity air flow in such a situation, would give rise to such a bundle of stagnation points, each of which is endowed with the same pressure head, thereby rendering the plane of impaction an equipotential plane.
  • each stream In a graded velocity air flow, each stream would impact with a different kinetic head, which reduces along a pre-determined axis, convert to an equivalent pressure head which also reduces correspondingly, thereby inducing the air to flow along a predisposed direction.
  • the low pressure zone is characterized by large frictional losses caused by eddies and vortices which are kept in motion by the shear-stress between this wake zone and the separated current.
  • FIG. 6 shows a beaker obstructing air flowing with uniform velocity.
  • a low pressure zone covering substantially the entire rear portion is formed.
  • Lateral boundary layer separation occurs just behind the upstream face causing streamlines to assume essentially synclastic paths.
  • those going over the upper edge accelerate in velocity, particularly as there is no pathway beneath the object. Once over the leaving edge, descent is visibly sharp.
  • the streamlines In gradient flow the streamlines, as shown in FIG. 8, divide asymmetrically both over and around the object.
  • the wake zone is both narrower and skewed and the turbulence anisotropic.
  • the streamlines asymptotically approach an axis which is parallel to the direction of air flow, but offset from the centre of the beaker towards the higher velocity air stream.
  • FIG. 10 shows a vertical configuration, comprising a blower 8, intake filter 9, plenum 10 and a final filtering device 1, the work space being bounded by containment surfaces such as a perforated table 11, back panel 12 and side panels 13, with access to a work space W.
  • the velocities are graded to increase in magnitude towards the front of the workspace with the object of retaining air stream linearity across the open working access.
  • FIG. 11 shows the axes of operation in relation to FIG. 10.
  • FIG. 12 shows the air flow streamlines that would affect particulate trajectories.
  • the presence of an object 6 gives rise to a turbulent zone T and a non-linear velocity zone C.
  • the corresponding turbulent zone by object 6 is of greater extent than T and the non-linear velocity zone greater than C.
  • FIGS. 14 and 15 plot typical curves for different trajectories followed by spherical particulates having a specific gravity of 2.0. Particulate contaminants when introduced into air streams trace a parabolic trajectory until they attain their terminal velocity thereafter, where all streamlines are of equal and constant velocity, they exhibit a more or less straight line of descent.
  • this locus concaves upwards owing to the progressively increasing velocities encountered along the path of descent under gravity.
  • the increase in velocity U with downward movement along the vertical axis in this way counteracts the adverse effects of an energy differential transverse to the X-axis to which the particulates are subject.
  • FIG. 16 illustrates another embodiment of the invention, being an arrangement to continuously sterilize and depyrogenate glass containers 14 for sterile pharmaceutical formulations, by means of pre-heated air passing through a filtering device 1H located in a housing 15 of a sterilizing zone 16.
  • Containers 14 are transported in a conveyor 17 under graded air flow achieved by means of the filtering device 1H and a blower 18. They are heated to temperatures above 300° C. The containers 14 are further transported on the same conveyor 17 to a cooling zone 19. In this zone they are cooled by graded air streams from filtering device 1C and blowers 20, located in a housing 21, which is segregated from the sterilizing zone housing 22.
  • the hot air stream gradient is so oriented that the highest velocity impacts on the coolest containers.
  • the hottest containers receive higher velocity, but at the end of the cooling cycle, consistent with FIG. 16, a higher velocity is oriented to ensure better control of airborne particulates, as the containers at this stage 23, are vulnerable to microbial contamination.
  • FIG. 17 shows comparative curves for the temperature cycle that the containers undergo during sterilization.
  • the abscissa represents the residence time within each zone, which is a function of the rate of travel of the conveyor.
  • the ordinate represents the temperature of containers when subjected to airstreams at 350° C.
  • the heat available for transfer along the axis of container transport is a function of both the differential in temperature of the air and containers, and the air volume striking the containers, that is, the air velocity. This explains the reduction in both the heating-up and cooling-down time as shown in the figure, yielding faster container throughputs, when multiple velocities are graded both the precise thermal energy transfer as well as for improved control over potential airborne contaminants.
  • the broken line represents the temperature cycle the same containers undergo with single velocity air streams at identical air temperature.
  • FIG. 18 shows as embodiment of filtering device which, as detailed by FIG. 19, comprises a continuous filter medium 5, pleated around separators 24, each pleat of which is supported by a wider separator with a progressive increment ranging up to 10 mm, such that they support and separate the pleats 25 formed around them and channel the air.
  • the assembly is housed in a frame 26 and sealed to prevent bypass around the medium.
  • the increase in surface area of successive pleats correspondingly increases the air quantity that passes through each pleat as the pressure differential and traverse air velocity across the medium 5 are constant.
  • This air is channelled by the separators to the projected filter face, where this variable volume yields graded velocities in overlapping steps and these velocities increase with each pleat.
  • FIG. 20 where the exit air velocities plotted against the pleat run, are given for both the ⁇ Y ⁇ and ⁇ Z ⁇ axes, with the broken line representing uniform velocity flow at 30 meters per minute.
  • the pleated filter grading means can be replaced by another form of grading means which may or may not be a filter. It could be, for example, a filter member having a thickness which increases progressively from one edge of the membrane to an opposite edge, the membrane being arranged across the gas flow upstream of the work station.
  • a foraminated grille could be employed as the grading means, with the open area of the foramination array increasing progressively from one edge of the grille to an opposite edge.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Ventilation (AREA)
  • Filtering Of Dispersed Particles In Gases (AREA)
  • Workshop Equipment, Work Benches, Supports, Or Storage Means (AREA)
US06/323,571 1981-04-09 1981-11-20 Method and apparatus for control of gas-borne particulates Expired - Lifetime US4412849A (en)

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
GB8111175A GB2098317B (en) 1980-11-24 1981-04-09 Method and device for control of airborne particles
GB8111175 1981-04-09
GB8113173 1981-04-29
GB8113173A GB2092296B (en) 1980-11-24 1981-04-29 Method of and apparatus for controlling gas-borne particulates

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US (1) US4412849A (enrdf_load_stackoverflow)
EP (1) EP0062719B1 (enrdf_load_stackoverflow)
JP (1) JPH0315085U (enrdf_load_stackoverflow)
DE (1) DE3175427D1 (enrdf_load_stackoverflow)

Cited By (13)

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Publication number Priority date Publication date Assignee Title
US4770680A (en) * 1986-05-19 1988-09-13 Fujitsu Limited Wafer carrier for a semiconductor device fabrication, having means for sending clean air stream to the wafers stored therein
US5027694A (en) * 1989-08-23 1991-07-02 The United States Of America As Represented By The Secretary Of The Department Of Health And Human Services Variable air flow eddy control
US5518450A (en) * 1991-09-24 1996-05-21 Overseas Publishers Association Method and apparatus for protecting uultraclean surfaces
WO2000064562A1 (en) * 1999-04-28 2000-11-02 Stratotech Corporation Adjustable clean-air flow environment
SG88724A1 (en) * 1995-10-13 2002-05-21 Jenoptik Jena Gmbh Management for generating a purified, low-turbulence air flow for supplying local clean rooms
US20030150328A1 (en) * 2001-03-20 2003-08-14 Tomas Hansson Air-cleaning device and method for arranging air cleaning in sensitive environments
FR2865406A1 (fr) * 2004-01-22 2005-07-29 Acanthe Diffuseur a effet parietal
US20090183635A1 (en) * 2008-01-17 2009-07-23 Vijayakumar R Combination high efficiency particle and gas filter
US20100267321A1 (en) * 2007-06-22 2010-10-21 Institute Of Occupational Safety And Health, Council Of Labor Affairs, Executive Yuan Air curtain-isolated biosafety cabinet
US20110038771A1 (en) * 2009-08-11 2011-02-17 Basf Corporation Particulate Air Filter With Ozone Catalyst and Methods of Manufacture and Use
US8499764B2 (en) 2010-05-26 2013-08-06 The Invention Science Fund I, Llc Portable apparatus for establishing an isolation field
US20140179212A1 (en) * 2008-09-30 2014-06-26 The Boeing Company Personal ventilation in an aircraft environment
US12116133B2 (en) 2021-06-30 2024-10-15 The Boeing Company Ventilation assembly in an aircraft

Families Citing this family (4)

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US4530272A (en) * 1984-01-13 1985-07-23 International Business Machines Corporation Method for controlling contamination in a clean room
FR2622960B1 (fr) * 1987-11-16 1990-03-23 Bardet Guy Unite de production de flux laminaire sterile a circulation verticale
NL8900390A (nl) * 1989-02-17 1990-09-17 Clean Air Techniek Inrichting voor het stofarm houden van een ruimte en clean room voorzien van een dergelijke ruimte.
NL2000530C2 (nl) * 2007-03-08 2008-09-09 Martin Van Schaik Gebouw voorzien van een werkplek, alsmede systeem en werkwijze voor het stofarm houden van de werkplek.

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US3336855A (en) * 1965-12-30 1967-08-22 Atmos Tech Corp Ultraclean work station
US3776121A (en) * 1972-06-23 1973-12-04 A Truhan Controlled environmental apparatus for industry
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GB1527116A (en) 1974-09-19 1978-10-04 Svenska Flaektfabriken Ab Surface treatment plant
GB1477570A (en) 1974-12-05 1977-06-22 Flanders Filters Flow control apparatus for air filters
GB1538862A (en) 1975-11-21 1979-01-24 Dechosal Sa Ets Enclosed locality and a process for filtering out micro-organisms in suspension in the air of the enclosed locality
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Cited By (19)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4770680A (en) * 1986-05-19 1988-09-13 Fujitsu Limited Wafer carrier for a semiconductor device fabrication, having means for sending clean air stream to the wafers stored therein
US5027694A (en) * 1989-08-23 1991-07-02 The United States Of America As Represented By The Secretary Of The Department Of Health And Human Services Variable air flow eddy control
US5302151A (en) * 1989-08-23 1994-04-12 The United States Of America As Represented By The Department Of Health And Human Services Variable air flow eddy control
US5518450A (en) * 1991-09-24 1996-05-21 Overseas Publishers Association Method and apparatus for protecting uultraclean surfaces
SG88724A1 (en) * 1995-10-13 2002-05-21 Jenoptik Jena Gmbh Management for generating a purified, low-turbulence air flow for supplying local clean rooms
WO2000064562A1 (en) * 1999-04-28 2000-11-02 Stratotech Corporation Adjustable clean-air flow environment
US20030150328A1 (en) * 2001-03-20 2003-08-14 Tomas Hansson Air-cleaning device and method for arranging air cleaning in sensitive environments
US6811593B2 (en) * 2001-03-20 2004-11-02 Toul Meditech Ab Air-cleaning device and method for arranging air cleaning in sensitive environments
FR2865406A1 (fr) * 2004-01-22 2005-07-29 Acanthe Diffuseur a effet parietal
WO2005080883A1 (fr) * 2004-01-22 2005-09-01 Acanthe Diffuseur a effet parietal
US20100267321A1 (en) * 2007-06-22 2010-10-21 Institute Of Occupational Safety And Health, Council Of Labor Affairs, Executive Yuan Air curtain-isolated biosafety cabinet
US20090183635A1 (en) * 2008-01-17 2009-07-23 Vijayakumar R Combination high efficiency particle and gas filter
US7998259B2 (en) * 2008-01-17 2011-08-16 Rajagopal Vijayakumar Combination high efficiency particle and gas filter
US20140179212A1 (en) * 2008-09-30 2014-06-26 The Boeing Company Personal ventilation in an aircraft environment
US10029797B2 (en) * 2008-09-30 2018-07-24 The Boeing Company Personal ventilation in an aircraft environment
US20110038771A1 (en) * 2009-08-11 2011-02-17 Basf Corporation Particulate Air Filter With Ozone Catalyst and Methods of Manufacture and Use
CN102548636A (zh) * 2009-08-11 2012-07-04 巴斯夫公司 使用臭氧催化剂的微粒空气过滤器和制备方法及用途
US8499764B2 (en) 2010-05-26 2013-08-06 The Invention Science Fund I, Llc Portable apparatus for establishing an isolation field
US12116133B2 (en) 2021-06-30 2024-10-15 The Boeing Company Ventilation assembly in an aircraft

Also Published As

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EP0062719B1 (en) 1986-10-01
EP0062719A1 (en) 1982-10-20
DE3175427D1 (en) 1986-11-06
JPH0315085U (enrdf_load_stackoverflow) 1991-02-15

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